Experimental Hybridizing 87 
extracted albinos give always albinos. Only 2 out of 94 
waltzed. (2) The dark-eyed mice with colored coats belonging 
to the middle term of the Mendelian series should also give, if 
inbred, the three types again in the proportion of 1:2:1. In 
this connection Darbishire points out that on Galton’s law of 
inheritance the farther the individuals of this middle class are 
removed from the first class, the fewer the albinos that should 
appear, since they are farther removed from the original ances- 
tor that was white. On the Mendelian law the members of 
this middle term should always continue to give the same pro- 
portion, 1:2:1. Experiments that Darbishire made to test this 
point seemed to show that the results follow more nearly the 
expectation of Galton’s law; but the purity of the types used 
may have seriously affected his results. 
Especially interesting, it seems to me, are Darbishire’s experi- 
ments with the extracted mice of the second generation having 
pink eyes and colored coats. If these are really pure, they should, 
if paired with pure albinos, produce animals similar to those of 
the parent cross between colored mice with pink eyes and 
albinos, z.e. there should be produced only spotted mice with 
dark eyes. This, however, was not the result obtained. Of 
98 young, 12 were albinos, while one pink-eyed (colored) indi- 
vidual also appeared. These results are complicated by the 
fact that the albinos used were also the extracted offspring 
of hybrids paired with albinos. Nevertheless, even granting 
this, it offers no explanation of why albinos should appear, and 
the only explanation that seems reasonable is that the albino, 
latent in the pink-eyed mice, has affected the result, pre- 
sumably being brought out again by crossing. Sixty-three of 
the 98 young were obtained from such contaminated albinos 
(extracted recessives). Only seven of the unions were between 
such pink-eyed mice and albinos which did not contain pink- 
eyed, spotted waltzers in their immediate ancestry. From these 
pairs 35 young were obtained, of which 10 were albinos —a 
relatively higher number of albinos, and approximately one 
fourth of the whole. The results seem to show that the extracted 
